Field of Invention
The present invention relates to a light source, and more particularly to an LED light source for headlamp of a motor vehicle.
Description of Related Arts
In the disclosed conventional art, the advanced structures with practical value of the LED headlamp developed all over the world are summarized as follows.
1. Multiple Lens Groups Type
One condenser and one LED form a lens group. The lens group projects a light beam for lighting a light spot on a screen. According to standard requirements for lower beam or upper beam, the light spots generated by multiple lens groups are combined into a light band, so as to meet illumination distribution requirements. This type of structure has a large size, a high price and a difficult process.
2. Free-Face Optical Lens Type
The headlamp comprises a condenser and an LED. However, the condenser is not a surface of revolution, but a free-form surface, in such a manner that the light spots generated by projection of the light beam comply with the illumination standard. This type of structure requires an extremely high luminous density of the LED, wherein the luminous density is an Lm/mm2 value of the luminous surface. This type of structure can be applied in lower headlight, but is difficult to be applied in upper beam.
3. Half Transparent and Half Reflecting Type
This type has same structure as a lens-type HID lamp, wherein the LED only serves as half of an HID lamp which is cut along an axis thereof. This type of structure is only suitable for the lower headlight.
The structures mentioned above reflect a concept that LED is implied as pointolite in the design idea. Therefore, applying the conventional structures of the HID lamp can not obtain satisfactory results.
The LED light source is a typical area light source. A maximum luminous density of a single LED is 100 Lm/mm2, which is practically impossible to reach 200 Lm/mm2. The luminous density of the HID is more than 1000 Lm/mm2, and furthermore, the luminous density of a halogen lamp is more than 400 Lm/mm2.
Therefore, with the LED for serving as a light source, the structures mentioned above are complicated and utility rate of luminous energy thereof is low.